1. Field of the Invention
The present invention relates to a method for producing a silicon single crystal wafer for particle monitoring having few pits on its wafer surface with high productivity.
2. Related Art
Particles adhered to a silicon single crystal wafer used for semiconductor devices may cause pattern breakage or the like during the production of semiconductor devices. In particular, because the pattern width of the most advanced devices (64M DRAM) is extremely small, i.e., 0.3 .mu.m, production of such patterns suffers from abnormalities (failure) such as pattern breakage even by the presence of particles of 0.1 .mu.m, and its production yield in the production of devices is markedly reduced. Therefore, particles adhered to silicon wafers must be decreased as far as possible.
To this end, in the production process of silicon wafers, particle counters are used to strictly control such particles (search of generation source, evaluation of cleaning effect, control of clean level of clean room, inspection of final products before shipment, etc.).
The measurement method of conventional particle counters involves, for example, irradiating a laser beam spot of around 10-100 .mu.m on a wafer for monitoring of which particles are measured (wafer for particle monitoring), and effectively condensing feeble lights scattered by the particles through multiple optical fibers, integrating spheres or the like, which condensed lights are converted into electric signals by photoelectric devices. Therefore, conventional particle counters count the number of spots (bright spots) on the wafer surface where light scattering is caused.
By the way, minute crystal defects are generated during the growth of silicon single crystals, and they do not disappear during the cooling of crystals, and remain in the processed and produced wafers as they are. When these wafers are cleaned in a mixed solution of aqueous ammonia (NH.sub.4 OH+water) and aqueous hydrogen peroxide (H.sub.2 O.sub.2 +water) as generally conducted so as to remove the particles, hollows (pits) are formed on the wafer surfaces because etching rate is faster in the crystal defect sites (such pits are called crystal originated particles, COPs).
If such silicon wafers are used as wafers for particle monitoring, and particle number is counted on such wafers by the above particle counter, light scattering by not only particles actually adhered to the wafer surfaces, but also light scattering by such pits are detected. Thus, there has been a disadvantage that a true particle number cannot be obtained.
In particular, it has been known that a wafer produced from a silicon single crystal pulled by the CZ method generates much more COPs compared with a wafer produced from a silicon single crystal produced by the floating zone melting method (FZ method) and an epitaxial wafer comprising a wafer produced by the CZ method on which a silicon single crystal thin film is grown.
On the other hand, it has also been known that, in order to decrease crystal defects (COPs) introduced into silicon single crystals during their growth in the CZ method, marked improvement can be obtained by using an extremely low crystal growth rate (for example, 0.4 mm/min or less; see, for example, Japanese Patent Application Laid-open No. 2-267195).
However, if the crystal growth rate is simply lowered from the conventional rate of 1 mm/min or more to 0.4 mm/min or less, the productivity of single crystals would be halved or further reduced, and the cost would be markedly increased, even though COPs may be improved. This remained as a problem not only in the production of wafers used for devices, but also in the production of wafers for particle monitoring used for particle measurement.